chore: still keep ctx in git.Repository struct for cat-file batch command (#38684)

Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.

If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.

http://localhost:3000/-/admin/monitor/perftrace

* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)

modules/git/commit_sha256_test.go

@@ -56,7 +56,7 @@ signed commit`
 		0x94, 0x33, 0xb2, 0xa6, 0x2b, 0x96, 0x4c, 0x17, 0xa4, 0x48, 0x5a, 0xe1, 0x80, 0xf4, 0x5f, 0x59,
 		0x5d, 0x3e, 0x69, 0xd3, 0x1b, 0x78, 0x60, 0x87, 0x77, 0x5e, 0x28, 0xc6, 0xb6, 0x39, 0x9d, 0xf0,
 	}
-	gitRepo, err := OpenRepositoryLocal(filepath.Join(testReposDir, "repo1_bare_sha256"))
+	gitRepo, err := OpenRepositoryLocal(t.Context(), filepath.Join(testReposDir, "repo1_bare_sha256"))
 	assert.NoError(t, err)
 	assert.NotNil(t, gitRepo)
 	defer gitRepo.Close()
@@ -99,7 +99,7 @@ signed commit`, commitFromReader.Signature.Payload)
 func TestHasPreviousCommitSha256(t *testing.T) {
 	bareRepo1Path := filepath.Join(testReposDir, "repo1_bare_sha256")
 
-	repo, err := OpenRepositoryLocal(bareRepo1Path)
+	repo, err := OpenRepositoryLocal(t.Context(), bareRepo1Path)
 	assert.NoError(t, err)
 	defer repo.Close()